TITLE: Flexible ceramic tape and method of making same
United States Patent 4329271
ABSTRACT:
An improved flexible ceramic tape consists essentially of ceramic
powder and a water soluble binder of polyacrylic acid polymer and
glycerol. Additions of small amounts of polyvinyl pyrrolidine to this
binder improves the flexibility of the resulting tape. The ceramic
powder consists of alumina. The invention also comprehends the method
of making this tape consisting of the steps of preparing a slip or
mixture of an aqueous solution of polyacrylic acid polymer and glycerol
together with the ceramic powder, casting this slip on a substrate to a
predetermined uniform thickness, and drying the mixture. The tape may
be removed from the substrate or allowed to remain mounted on it.
INVENTORS:
Kemr, Miro (San Francisco, CA)
Mizuhara, Howard (San Mateo, CA)
APPLICATION NUMBER: 06/216240
PUBLICATION DATE: 05/11/1982
FILING DATE: 12/15/1980
ASSIGNEE: GTE Products Corporation (Stamford, CT)
PRIMARY CLASS: 524/386
OTHER CLASSES: 524/430, 524/556
INTERNATIONAL CLASSES: C08K3/22; C08K5/053; (IPC1-7): C08K5/05; C08K5/13
FIELD OF SEARCH: 260/33.4R, 260/42.11
US PATENT REFERENCES:
3991029 Ceramic compositions and articles made therefrom November, 1976
Adelman 260/42.11
2853461 Ceramic binder comprising a nitrogen containing salt of a
synthetic resin September, 1958 Padbury et al. 260/42.11
2765507 Sand core and mold composition and method of making cores and
molds therefrom October, 1956 Wolf et al. 260/42.11
PRIMARY EXAMINER: Schofer, Joseph L.
ASSISTANT EXAMINER: Sarofim N.
Attorney, Agent or Firm:
Lawler, John F.
CLAIMS:
What is claimed is:
1. A flexible ceramic composition consisting, in dry weight, of 2-4%
polyacrylic acid polymer having a molecular weight of approximately
450,000, 9-14% glycerol and the balance a ceramic substance consisting
of alumina.
2. A flexible ceramic composition consisting, in dry weight, of 2-4%
polyacrylic acid polymer having a molecular weight of approximately
450,000, 9-14% glycerol, 0.5-2% polyvinyl pyrrolidine, and the balance
alumina.
3. The method of preparing a flexible ceramic tape consisting of the
steps of preparing a mixture consisting of an aqueous solution of, in
dry weight, 2% to 4% polyacrylic acid polymer having a molecular weight
of approximately 450,000 and 9% to 14% glycerol and the balance alumina
powder, casting said mixture to a uniform thickness on a substrate, and
drying said mixture.
4. The method of preparing a flexible ceramic tape consisting of the
steps of preparing a mixture consisting of an aqueous solution of, in
dry weight, 2% to 4% polyacrylic acid polymer having a molecular weight
of approximately 450,000 and 9% to 14% glycerol and 0.5% to 2.0%
polyvinyl pyrrolidine and the balance alumina powder, casting said
mixture to a uniform thickness on a substrate, and drying said mixture.
DESCRIPTION:
BACKGROUND OF THE INVENTION
This invention relates to an improved flexible ceramic tape and method
of making same.
The advantage and utility of flexible ceramic tapes are in part
measured by the organic content of the binder which holds the ceramic
powder together. Prior practice in the ceramic tape industry has been
to use polyvinyl butyral as a binder, dioctyl phthalate as a
plasticizer and solvents such as the hydrocarbons xylene and toluene
and other organic material such as trichlorethylene and alcohol. The
difficulty with this prior art practice is that the toxic nature of the
solvents requires special solvent scrubber apparatus to prevent the
vapor from being expelled into the atmosphere during the drying
process. In addition, since these solvents are petroleum derivatives,
the price of the solvent has been increasing and its availability is
not always assured.
Other tape binder systems used in the past include polyvinyl alcohol
with plasticizers such as glycerine, polyethylene glycol and ethylene
glycol but the total organic content of such binders including the
plasticizer range from 20% to 25% of ceramic dry weight. Because of the
high volume to weight ratio of the polyvinyl alcohol in such systems,
control of the tape preparation process during the burnout period is
very critical, the high organic content tending to produce uncontrolled
release of gases which adversely affects the structure and quality of
the tape.
This invention is directed to a ceramic tape composition and a method
of manufacturing it which avoid the foregoing problems.
A general object of this invention is the provision of a flexible
ceramic tape which contains a relatively low proportion of organic
components.
A further object is the provision of a method of making flexible
ceramic tape using a water soluble binder having a relatively low
quantity of organic components.
These and other objects of the invention are achieved with a binder
consisting of, in dry weight, 2-4% polyacrylic acid polymer, 9-14%
glycerol and the balance a ceramic consisting of alumina. The invention
also comprehends the method of making the flexible ceramic tape.
In accordance with this invention flexible ceramic tape is made with
polyacrylic acid polymer having a molecular weight of approximately
450,000 in combination with glycerol and, optionally, polyvinyl
pyrrolidine, and mixed with a ceramic powder consisting of alumina.
A preferred composition of a flexible ceramic tape consists of, in dry
weight, 3% polyacrylic acid polymer, 12.5% glycerol and the balance
alumina. Satisfactory results are obtained with the tape having, in dry
weight, 2-4% polyacrylic acid polymer, 9-14% glycerol and the balance
alumina.
The flexible tape and its binder system were evaluated by mixing a
fixed quantity of ceramic powder with each of several binder systems
having different proportions of ingredients. The mix was milled for 20
hours and cast from a dispenser with a 0.065" knife opening onto a
substrate consisting of Mylar film. The wet tape was then dried at 90°
C. for 1 hour and thereafter punched into a square sheet measuring
37/8"×37/8"×0.038" thick which was air fired at 1575° C. for 3 hours.
After firing, the tape sheet had dimensions of 31/4"×31/4"×0.033" thick
and a density of 3.70 g/cc.
Alumina was used in these tests and had a composition consisting of the
following (in percent by weight):
66.9 reactive alumina, average particle size 1.7μ
28.6 reactive alumina, average particle size 0.7μ
3.5 talc (magnesium silicate)
1.0 refined clay
The binder system with which the alumina was mixed consisted of, in dry
weight, 0.25% of a deflocculating agent (sold as Darvan C by R. T.
Vanderbilt Co., New York), 22% water, 0.01% of a dispersant (sold as
Dispex A-40 made by Allied Colloid Co., Yorkshire, England, X% of
polyacrylic acid polymer having a molecular weight of about 450,000
(sold as Carbopol 907 by B. F. Goodrich Co., Ohio) and Y% glycerol,
with X being 2-4 and Y being 9-14. The molecular weight is determined
by the intrinsic viscosity method.
Flexibility of green tape varied somewhat with variations in
ingredients as described in Table I.
TABLE I
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Carbopol 907 Glycerol 2% 3% 4%
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10 Moderately Moderately Moderately
brittle tape
brittle tape
stiff
11 Moderately Good Tape Slightly
brittle tape
slightly stiff
brittle
12.5 Soft tape Good tape, Moderately
and short* slightly soft
stiff
15 Tacky Tacky Tacky
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*Tends to crumble
While tacky tape is generally not as desirable as nontacky tape, the
former may be used with utility and advantage in the formation of
multilayer substrate.
Tape produced in accordance with this invention and sintered had an
excellent finish, in the range of 15-20μ in. (measured in accordance
with the procedure described in USA Standard B46-1962), was
satisfactorily flat (2-3 mils per inch) and dense, had no bubbles or
blisters and was almost porefree.
Further tests of the mixture containing, in dry weight, 3% polyacrylic
acid polymer, 12.5% glycerol, and balance alumina were made by the
addition of 0-5% polyvinyl pyrrolidine (PVP) sold as K-60 by GAF
Corporation, New York. The effect of such PVP additions on tape
characteristics are listed in Table II.
TABLE II
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% BY WEIGHT
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0.5 No noticeable improvement
1.0 Improved flexibility
1.5 Improved flexibility
2.5 No greater improvement
3.0 No greater improvement
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